1. Technical Field
A method for fabricating a semiconductor device, and in particular to an improved method for forming a storage node electrode of a high integration semiconductor device is disclosed.
2. Description of the Background Art
Recently, reductions in cell surface area and operation voltage have been actively investigated in order to achieve a highly integrated semiconductor device. In a highly integrated semiconductor device, the area of a capacitor is sharply reduced. Therefore, it is required to increase charges for the operation of the memory device, namely capacitance per unit area.
On the other hand, the capacitor for a memory cell basically consists of a storage node electrode, a dielectric film and a plate node electrode. A useful capacitor for obtaining high capacitance in a small area has a desired characteristic: a dielectric film that is thin, with an effective area is increased by the three-dimensional structure of the capacitor, or the dielectric film is composed of a material having a high dielectric constant.
In general, when a leakage current is decreased and a breakdown voltage is increased, the capacitor obtains a good dielectric film. However, when the dielectric film has a thickness of less than 100 xc3x85, the leakage current is increased due to a phenomenon known as Fowler-Nordheim tunneling, thereby reducing reliability. In addition, a method for using the material having the high dielectric constant in the memory cell capacitor has been investigated, so that high capacitance can be obtained. even in the small area of the high integration memory device. At last, a method for increasing an area of the storage node electrode through the three-dimensional structure has been suggested to increase the effective area of the capacitor.
A semiconductor device such as 256M DRAM has normally employed an inner cylinder type storage node electrode. A conventional method for forming the inner cylinder type storage node electrode will now be described with reference to the accompanying drawings.
FIGS. 1a to 1d illustrate sequential steps of the conventional method for forming the storage node electrode of the semiconductor device.
One preferred example of the conventional method uses a polysilicon hard mask. Referring to FIG. 1a, a contact plug 14 is formed in an interlayer insulation film 12 of a semiconductor substrate 10 where a predetermined device structure has been formed. Thereafter, etch stop films 16, 18, a sacrificed insulation film 20, a polysilicon hard mask 22 and a reflection stop film 24 are sequentially stacked on the whole surface of the interlayer insulation film 12 where the contact hole 14 has been formed. Here, reference numeral 16 denotes a nitride film which serves as the etch stop film of the sacrificed insulation film 20, and reference numeral 18 denotes a high density plasma (HDP) film which serves as the etch stop film and dip-out of the sacrificed insulation film 20.
As illustrated in FIG. 1b, in order to provide a region for the storage node electrode, an opening 26 is formed by etching the hard mask 22xe2x80x2, the sacrificial insulation film 20xe2x80x2 and the etch stop film 18xe2x80x2. According to the etching process, the reflection stop film 24 is removed, and the polysilicon hard mask 22xe2x80x2 is partially etched. The etch stop film 16 remains unaltered.
Referring to FIG. 1c, if etching the hard mask 22xe2x80x2 remains on the resultant structure where the opening 26 has been formed, the sacrificial insulation film 20xe2x80x2 is partially damaged. Thereafter, when the etch stop film 16xe2x80x2 is patterned to expose the surface of the contact plug, the sacrificial insulation film 20xe2x80x2 is damaged again. The loss of the sacrificial insulation film 20xe2x80x2 influences the height of the inner cylinder type storage node electrode. Therefore, when the hard mask film 22xe2x80x2 and the etch stop films 16xe2x80x2, 18xe2x80x2 are removed, the loss of the sacrificial insulation film 20xe2x80x2 must be minimized.
As depicted in FIG. 1d, a conductive material is deposited on the opening 26, thereby forming the inner cylinder type storage node electrode 28. A filling film (not shown) is formed to fill up the opening part 26, and its surface is polished. Thereafter, the sacrificial insulation film 20xe2x80x2 is removed, and a dielectric film 30 and a plate node electrode 32 are sequentially formed on the storage node electrode 28. Thus, fabrication of the capacitor is finished.
As described above, when the hard mask film and the etch stop film are removed, the inner cylinder type storage node electrode 28 is excessively damaged. As a result, the area of the storage node electrode is decreased, and thus capacity of the capacitor is also reduced.
FIGS. 2a and 2b illustrate sequential steps of another conventional method for forming a storage node electrode of a semiconductor device, which has been thought to reduce the loss of the sacrificed insulation film.
As illustrated in FIG. 2a, the hard mask film 22, the sacrificial insulation film 20xe2x80x2 and the etch stop films 18xe2x80x2, 16xe2x80x2 which are stacked as in the above-described method are etched to form the opening.
Thereafter, the inner cylinder type storage node electrode 28 is formed by depositing the conductive material on the resultant structure. The filling film 29 is formed to fill up the opening part. Then, the whole surface is polished according to a chemical mechanical polishing process.
As shown in FIG. 2b, the polishing process is performed until the hard mask 22xe2x80x2 is removed. At this time, a cell region 100 has higher density than a peripheral region 200, and thus a polishing speed of the cell region is increased. As a result, a T-shaped step is formed between the peripheral region 200 and the cell region 100.
Therefore, the capacity of the capacitor is much smaller in the cell region than the peripheral region. Accordingly, the method using the chemical mechanical polishing process increases the step between the peripheral region and the cell region, and reduces the capacity of the capacitor in the cell region, thereby deteriorating the property of the device.
A storage node electrode of a semiconductor device is disclosed, which prevents an etch step of a sacrificial insulation film between a peripheral region and a cell region, and which minimizes an etch loss of the sacrificial insulation film. The disclosed method involves forming an opening part for the inner cylinder type storage node electrode, forming the storage node electrode and a filling film for filling up the opening, etching the resultant structure until a polysilicon hard mask reaches a predetermined thickness, and removing the hard mask according to a chemical mechanical polishing process.
A disclosed method for forming a storage node electrode of a semiconductor device comprises: forming a contact plug in an interlayer insulation film on a semiconductor substrate where a predetermined device structure has been formed; sequentially stacking at least one etch stop film, a sacrificial insulation film, a polysilicon hard mask and a reflection stop film on the whole surface of the interlayer insulation film where the contact plug has been formed; forming an opening in the hard mask, the sacrificial insulation film and the etch stop films to remove the reflection stop film to obtain a storage node electrode region; forming a storage node electrode by depositing a conductive material over the resultant structure where the opening has been formed; forming a filling film for filling up the opening; etching the filling film, the storage node electrode and the hard mask so that the hard mask has a predetermined thickness; and etching the resultant structure according to a chemical mechanical polishing process so that the residual hard mask can be completely removed.
The method for forming the storage node electrode of the semiconductor device may further include forming etch preventive films, before forming the storage node electrode by depositing the conductive material over the resultant structure where the opening part has been formed.
The etching of the resultant structure so that the hard mask has a predetermined thickness may be performed by using fluorine or chlorine etching solution so that the hard mask becomes a residual target below 500xc3x85.
The etching of the resultant structure according to the chemical mechanical polishing process so that the residual hard mask can be completely removed is performed by using an abrasive of 50 to 300 nm and maintaining pH ranging from about 6 to about 11.